*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body{
    background-color: skyblue;
}
.container{
    width: 1200px;
    margin: 0 auto;
}
.col:first-child,.col:last-child{
    width: 33.333333%;
    float: left;
    height: 200px;
    background-color: saddlebrown;
}
.col:nth-child(2){
    width: 33.333333%;
    float: left;
    height: 200px;
    background-color: skyblue;
    border: 10px solid darkblue;
}
@media (max-width: 1200px) {
    body{
        background-color: slateblue;
    }
    .container{
        width: 100%;
    }
    .col{
        width: 100%;
    }
}
@media (max-width: 600px){
    body{
        background-color: seashell;
    }
    .container{
            width: 100%;
        }
    .col{
        width: 100%;
    }
}
.container:after{
    content: "";
    display: table;
    clear: both;
}